Extraordinary minds discuss ideas

Our cars can become very hot, especially if left parked for long periods under the direct sun. What ways can we use to reduce this heat? How effective are window tints? (photo from Misha (c) fotolia.com).

How effective are window tints in cooling our cars?

Update (Dec. 11, 2013): I wrote a series of two articles on the science of car window films:

Part 1 discusses why our car cabin warms up so rapidly and what methods we can use to cool the car cabin temperature.

Part 2 discusses how window films work and how to choose the right window film for our cars in Malaysia.

I recently had to replace my car’s front windshield which also meant I had to re-tint my windshield. I was curious exactly how effective are car tints in cooling our cars.

Yes, we know tints make our car cooler, but exactly by how much? If car tints are effective, why is it that some people curiously complain that their car tints, even reputable and expensive tints, do not “seem to work”? And my final burning question was: which side of our car windows allow in the most heat? Intuitively, the most critical car window should be the largest window piece which is the front windshield. The larger the window piece, the more the area is exposed to the sun, which in turn meant increasingly more heat would be let in. The manager from a car tint shop I asked confirmed this rationalization – but again, where is the evidence?

How hot can it get inside the car? How effective are tints anyway? (photo from images.quickblogcast.com)

But before I discuss about the effectiveness of car tints, I like to highlight that the colour of your car can make a significant impact on your car cabin temperature. In 2005, the TV show Mythbusters (Episode 38) measured the car cabin temperature of two exact car models, differing only in their colours: one was white and another black. These two cars were parked under the hot sun, and car cabin thermometers revealed that the black car was hotter than the white car by as much as 5 degrees Celsius.

Choose a white car. Mythbusters, a popular TV programme, showed that black cars can be hotter than white cars by as much as 5 degrees Celsius (photo from mythbusters.com).

A scientifically more rigorous experiment in 2011 by Levinson and associates confirmed that car colours do matter in terms of the amount of heat they let in. The difference in car cabin temperature between a black car and a silver car (same exact Honda car models) ranged between about 0.5 to 10.5 degrees Celsius, with an average between 4 to 5 degrees Celsius.

What these two works summarize is that even without tinting your car windows, you can reduce your car cabin temperature significantly, possibly by as much as 10 degrees Celsius, simply by choosing a lighter over a darker coloured car.

Our car cabin does not warm uniformly. In a typical hot day in Malaysia, the dashboard can reach a scorching 80 degrees Celsius, the front windshield 70 degrees Celsius, and the interior ambient air 50 degrees Celsius.

Car cabin does not warm uniformly, where the dashboard experiences the highest warming. Sunshade (placed behind the front windshield) lowered the temperature of the dashboard and front ambient air, but the sunshade had a less cooling effect on the rear windshield and rear ambient air (redrawn from Al-Kayiem et al., 2010).

Al-Kayiem and associates in 2010 found that using a reflective sunshade on the front windshield could reduce the dashboard and front windshield temperature by as much as 30 and 20 degrees Celsius, respectively. The front-placed sunshade could also cool the front ambient cabin air by as much as 10 degrees Celsius. Nevertheless, given enough time, the car cabin temperature under the protection of a sunshade would eventually reach the same heat levels as that without a sunshade protection. Without sun protection from the rear, a sunshade placed only in the front of the car had less cooling effect on the rear windshield and rear cabin.

The work by Jasni and Nasir in 2012 is interesting. Similar to that observed by Al-Kayiem and associates, they observed that the car dashboard temperature could reach a maximum of more than 80 degrees Celsius, and by using a sunshade (placed on all car windows, not just on the front window) could cool the dashboard by an average of 22 degrees Celsius (with a maximum reduction of 30 degrees Celsius).

Jasni and Nasir (2012) showed that sunshade (placed on all car windows) cooled the dashboard the most, but it had little cooling effect on the car ambient air (redrawn from Jasni and Nasir, 2012).

Average maximum temperature in the car cabin. Baseline is that without any car cooling methods (redrawn from Jasni and Nasir, 2012).

Average and maximum reduction in temperature by sunshade and tint compared to without any cooling methods (baseline) (redrawn from Jasni and Nasir, 2012).

Interestingly, window tinting did not cool the dashboard by as much as that cooled by the sunshade. Car tint cooled the dashboard by an average of only 7 degrees Celsius (with a maximum reduction of 12 degrees Celsius).

However, window tinting was more effective than sunshade in cooling the car cabin temperature (front and rear ambient air). There was little difference between the car cabin temperature with and without the sunshade protection. The sunshade only cooled the car cabin by an average of 2 degrees Celsius (with a maximum reduction of 6 degrees Celsius), whereas the tint cooled by an average of 5 degrees Celsius (with a maximum reduction of 8 degrees Celsius).

One could of course argue that using a tint with a higher heat rejection rate would cool more the car. The tint used by Jasni and Nasir is on the lower end of quality. The infrared rejection of the tint used by them was 85% for the front windshield and 65% for the rear windshield and all side windows (no TSER or Total Solar Energy Rejection values were given).

Unprotected against the sun, the car cabin temperature could be as high as nearly 60 degrees Celsius. So, even if a good quality tint could reduce the cabin temperature by as much as 10 to 15 degrees Celsius (nearly double that reported by Jasni and Nasir), the car cabin would still feel uncomfortably warm at about 45 to 50 degrees Celsius. Perhaps this is why some people feel that their car tint “does not appear to work”.

But which car window allows in the most heat? As mentioned earlier, I thought the front windshield, being the largest window piece, would allow in the most heat. Measurements by Al-Kayiem and associates confirmed my hypothesis. Measurements revealed that solar irradiance (that is, the amount of incoming energy from the sun) was the highest for the front windshield, followed by the rear windshield. Computer simulations further revealed that the hot spots within a car cabin are at the front and rear windshields, as well as the ambient air immediately beneath the car roof.

At the end, results from these two studies show that car-cooling methods like a simple sunshade and window tinting do work. Window tint is overall more effective than the sunshade in cooling the car cabin and that window tint cools the car cabin more uniformly than the sunshade. However, the sunshade is unexpectedly far more effective than tint in cooling the car dashboard.

So, here is the bottom line: if you are looking to cool your car cabin, choose a tint with a high heat rejection rate and place a reflective sunshade on the front windshield during parking. If you are on a tight budget, install a tint with a higher heat rejection rate on your front windshield, and if possible, on the rear windshield as well. The side windows can have lower heat rejection rates. Oh yes, and pick a light coloured car too. Caveat: bear in mind that such a setup is not perfect; it would not completely insulate your car from heat. You should still expect your car cabin to feel a little warm, perhaps even uncomfortably so, especially after long hours of parking under the burning sun.

Hi, I would like to get a good tinted for my new car, all good brands cost rm2300 and above. One of the “V” brand TSER just 35% only but cost rm2500! The windshield need at least VLT 70% and above? VLT 55% for windshield good for night view? Metal or ceramic better? I’m looking for a tinted can last for 10 years with reasonable price. Pls advice! Thanks!

When it comes to window tints, we get what we pay. Good tints cost a lot of money, but lousy tints, cheap. If you are tight on budget but still want good tints, I recommend installing good tints on the front windshield since that is the main source of heat entry into our cars. You can install cheaper tints on the side and rear windows. Then once you have saved enough, you can install good tints on the other windows. Note: ceramic tints are better.

Great article with lots of solid information! I would also like to point out that while standard dyed films can reject UV and visible light, there are films that reject IR (infrared) much better. Two types of higher heat rejecting film are metalized and ceramic.

Metalized films actually have a thin layer of metal and have been in use for a while. Unfortunately, they block cell phone reception so they are not used as much. Newer ceramic films have nanoparticles of ceramic embedded into the film, rejecting the IR but allowing radio waves from your phone to pass. Ceramic window films cost a little bit more, but considering that they typically reject two thirds of the IR, they are worth it!

Yes, of course, leaving some window gap will help to cool the car, even better if you fully wind down all windows or open all car doors! But having all windows and doors closed is for security purpose as well as to keep out outside dirt. Besides this article is specifically about effectiveness of car tints and parts of the car cabin that are the warmest. I have written two follow-up articles, one of which compares different car cabin cooling methods.

Thanks for sharing the post. Actually, I had gone through some articles on Internet that Special military film are also used in window for tinting and There’s also a data that illustrates that it will block 95% of UV rays entering into our car. What do you say about this ?

Good info sharing and research.
Is it recommend to install tint at the existing sunroof which is already dark glass?
If installed the tint with lowest VLT % for sunroof, will it contain the heat inside the car and become worst?

Yes, you should install tint on the sunroof as that window can be a source of heat. Install tint with the highest heat rejection, as indicated by the tint’s TSER reading. Lowest VLT means lower visibility (the less you can see out) but it also means lowest heat entry into your car. So installing a low VLT on the sunroof is good to reject heat but less visible light can get into your car.

Frankly, they are the same with one another. There was a test done some time ago, and they found the different tint were nearly the same with one another. If there was any difference, they are not noticeable by us.

No, rain should not affect tint installation provided the installation is done indoors and you do not wind down the windows after installation. Anyway, whenever we install tints, it is not recommended you wind down the windows for the next 2-3 days to ensure the tints properly adhere to the glass.

When it comes to tint, you get what you pay. Generally, the better the tint, the more expensive it will be as well. However, there are little differences between the best tint brands, so choose an authorized tint shop and see their range of tints. These shops usually have display test units.

Thanks for the article. I have just changed my car windscreen.
My previous tint was from a famous brand, but they did not give me their best tint, claiming that it is illegal.
Base on your experience, Which tint do you recommend for maximum effectiveness – highest TSER?
Thanks

Not only is the tint brand important but the shop you go to is also just as important because some shops can show you one brand but install another brand. Did you go to an authorized tint shop? Find another authorized tint shop and check the local car forums if there are any good or bad reviews or comments about the shop.

Frankly, all well known brands are the same or nearly the same with one another. Even if they are different, their difference is so slight that we can’t detect.

Hi, I been reading several postings on the car tinting as I need to install a good tinting for my new HRV. Basically, I am looking for one which can block off the heat, JPJ compliant, GPS & smart tag friendly, lasting and also a security tint. Can you please recommend me a good brand ?
Thanks

I am looking to tint my car. What can you recommend me? I want a tint that has the best heat rejection as I am afraid of heat. It would also be great if the visibility is great. Have had really disappointing tints which I had to pay an arm and a leg for in the

What I observed with tinting is that the heat of the windshield makes the car warm inside. Tints are installed inside the car, back of the windshield not at the front which is direct to the sun so they only block direct heat from the sun (radiation) and they tend to heat the windshield more. The heat inside the car is then caused by induction by the windshield. To really block heat then is to apply external tint which will then cools the windshield as well. Are there any available external tint for cars?

Any surface including tints will absorb some of the heat which will then radiate. That’s why when you touch the tint, it feels warm, just as touching a “naked” glass would feel warm. But try touching a naked glass and compare it with a surface covered with tint. Both surfaces feel warm, but the surface with the tint will feel less warm.

Applying tints will reduce the amount of heat in the car because it reflects a large portion of incoming heat away from the car, making the car cabin cooler, or at least, making it warm slower.

Yes, applying a tint outside the glass would make the glass cooler because it reduces the amount of heat reaching glass. But applying the tint outside has its challenges: the tint is exposed to rain which can slowly cause it to peel. There are some glass protection window films that are applied on the exterior of the windshield, not so much to reduce heat but to protect the windshield against stones that could break the glass. But such films are expensive because they are applied on the outside, so special glue and installation is required. If tints were to be applied on the outside, these tints would be more expensive, making them less competitive with cheaper tints which are applied internally.

Besides, applying a tint outside would probably cause only a small improvement in heat reduction considering that absorbed heat is only a small factor (<5%) in heating the car cabin.

Nice post. If you use the right film from a high-quality manufacturer you can definitely keep your car cooler. In addition to the aesthetic appeal of tinted windows you can also achieve heat and UV rejection. However, make sure you check local window tinting laws before you have your windows tinted, as they will differ state by state. For more information about window tinting please visit [link deleted].

Thanks for the videos. There have been some tests on these small cooling fans that act to draw out hot air and draw in cool air into the car cabin. However, these tests reveal very little to no cooling effect by the fans. In other words, they don’t work as they claim. You will need larger fans to be effective. Some cars periodically turn on their air con fan to draw in cool air and let out hot air.

The second video is interesting, but I wonder if just driving off with all car windows down would be better and faster to cool down the car?

Yes, that cooling fan is useless, this is an ancient product, my father used 20 years ago, no effect at all. What I want to show is starting from 1:15 which open 1 front window and 1 rear window. To be honest i tried yesterday, like no different with my previous matter – open 2 front windows. Anyway driving off with window(s) open will increase fuel consumption due to resistance increased and car need more power to move. Also, bring in more dust into car. Malaysia has very hot weather nowadays, so letting go few cents to have car reduce heat faster is worth. 🙂

Thanks for the share. True, dust gets in while driving with the windows down, but I do this only for a minute. The car cabin can cool down rapidly. But it is good to know I can “fan” the car cabin as well! But I am not sure about the door hinges if I do this all the time! 🙂

Yes, you could! But parking spots under trees aren’t always available. Moreover, parking under trees do have risks. No, I’m not talking about falling tree branches. 🙂 Bird poo and falling tree sap onto our car can etch into the paint, especially if they are left unclean for long periods. These paint etchings can be difficult to remedy.